The present invention relates to vacuum flitch tables in general and more particularly, the invention relates to self-cleaning vacuum valves for flitch tables that include a cutting edge for cutting debris caught in the valve.
In the veneer slicing industry, a flitch is carried on a flitch table for slicing. The flitch is held in place on the flitch table by a set of dogs and, typically, the table moves the flitch in a reciprocating motion past a slicing knife which slices the veneer from the flitch. Since the dogs extend upwardly from the flitch table as much as 3/4 inch or one inch, a substantial thickness of the heart of the flitch unavailable for slicing. Unfortunately, the best veneer comes from the heart of the flitch. Thus, the loss of 3/4 inch of a flitch to slicing represents a major loss of productivity.
Vacuum flitch tables have been proposed to overcome the problem by eliminating the need for the dogs. For example, U.S. Pat. No. 3,905,408 to Hale discloses a vacuum flitch table that includes a vacuum cell plate that incorporates a plurality of vacuum cells. Each vacuum cell is equipped with a check valve to open the cell to a vacuum source. When a flitch is placed on the flitch table, the flitch seals the vacuum cell and the check valve opens to admit vacuum to the cell and hold the flitch in place.
Unfortunately, conventional vacuum flitch tables suffer from a serious disadvantage in that the valves tend to get clogged up by debris from the flitch, such as dirt and splinters. One attempt to overcome the problem of clogged valves is disclosed in U.S. Pat. No. 5,385,184 to Mellor. The '184 patent discloses a vacuum flitch table that incorporates a ball valve to open each cell to the vacuum source and positions a screen between the flitch and the ball valve to keep the valve from clogging up with debris. However, the problem was not completely solved because the debris collection point was merely moved from the valve to the screen. The screen collects the debris and eventually clogs up. When the screen gets clogged up, an operator must unclog the screens, typically by actuating a blow-back system to blow the debris out of the screen by compressed air. Thus, such prior art systems involve lost worker productivity to unclog the screens and further requires a complicated and expensive blow-back system.